132 



EXPERIMENTAL PHYSIOLOGY. 



Other forms of batteries are used, but the foregoing are suffi- 

 cient for the purposes of these exercises. 



5. The Galvanoscope or Detector. 



(a.) Charge a Daniell's cell and attach a copper wire to 

 the negative pole (zinc), and another to the positive pole 



(copper). On bringing the 

 free ends of the two wires 

 together, the circuit is 

 made, and a current of 

 continuous, galvanic, or 

 voltaic electricity circulates 

 outside the battery from 

 the + to the - pole. The 

 existence of this electrical 

 current may be proved in 

 many ways e.g., by the 

 effect of the current on a 

 magnetic needle. 



(b.) Use a vertical gal- 



Fig. 35. Bichromate Cell. -A, the 

 glass vessel ; K, K, carbon ; Z, 

 zinc ; D, E, binding screws for 

 the wires; B, rod to raise or 

 depress the zinc in the fluid ; C, 

 screw to fix B. 



Fig. 36. Detector. 



vanoscope, or as it is called by telegraphists, a detector (Fig. 

 36), in which the magnetic needle is so loaded as to rest in 

 a vertical position. A needle attached to this moves over a 

 semi-circle graduated into degrees. Connect the wires 

 from the + and - poles of the Daniell's battery with 

 the binding screws of this instrument, and note that when 

 the circuit is made, the needle is deflected from its vertical 



